Why is it hilarious to Higgins that Eliza even mentioned marrying Freddy? (Act 5)

Higgins finds the idea funny because he's prepared her to marry nobility..... he says he won't have his "masterpiece" wasted on a man like Freddy. He finds it unthinkable.

HIGGINS [sitting down beside her] Rubbish! you shall marry an ambassador. You shall marry the Governor-General of India or the Lord-Lieutenant of Ireland, or somebody who wants a deputy-queen. I’m not going to have my masterpiece thrown away on Freddy.